1. Field of the Invention
The present invention relates to an electrophoresis apparatus, a method of electrophoresis and a capillary array in which a sample such as DNA labelled by a fluorescent material is separated, and such as base sequence thereof is detected and analyzed through electrophoresis in a plurality of capillaries.
2. Conventional Art
Electrophoresis using capillaries has been used for the purpose of such as determining base sequence and base length of DNA. A method of multi capillary electrophoresis using a plurality of capillaries is already known broadly and is disclosed in many patent documents. U.S. Pat. No. 5,366,608 discloses to increase density of capillaries at a detection portion of fluorescence from a fluorescently labeled sample in the capillaries than the capillary density at a sample introduction portion. U.S. Pat. Nos. 5,516,409 and 5,529,679 disclose to detect fluorescence from a fluorescently labeled sample to be discharged from capillaries in combination with the capillaries and flow cells. U.S. Pat. No. 5,582,705 discloses to dispose a detection portion of a capillary array on a mount, to remove a part of coating on the capillaries to form a light transmission portion for the capillary array and to irradiate laser beam from the side face of the light transmission portion to detect fluorescence. U.S. Pat. No. 5,790,727 discloses to dispose optical fibers at a detection portion of a capillary array to detect fluorescence wherein the vicinity of the detection portion of the capillary array is closely contacted to a V shaped groove assembly.
U.S. Pat. No. 4,985,129 discloses to dispose a single piece of a capillary wound in a coil shape in a housing and to provide a heat dissipation member in a room surrounding the capillary. However, the document does not take into account of a problem of heat concentration in a multi capillaries.
In an electrophoresis separation and analysis, a sample containing DNA which is the very object of measurement is injected into gel such as polyacrylamide in a glass capillary and a voltage is applied between both end portions of the capillary. DNA compounds in the sample migrate in the capillary and are separated depending on such as molecular weight thereof to produce DNA bands in the capillary. Since a fluorescent dye is added to the respective DNA bands, the respective DNA bands are colored through irradiation of laser beam, therefore, the color is read with a fluorescent detection means to determine DNA sequence. Herein, in order to enhance resolution of DNA through electrophoresis it is important to keep the capillary at a predetermined temperature, for example, at 50° C. over the entire period of electrophoresis. This is because the migration speed of DNA in gel has to be kept constant at the above predetermined temperature.
As temperature control methods of capillaries in a capillary electrophoresis apparatus, the following methods have been used, in that a contact temperature adjustment method in which the capillaries are contacted to a temperature control plate provided in the electrophoresis apparatus; an air conditioning method in which temperature adjusted gas such as air is circulated in a thermostatic oven provided in the electrophoresis apparatus and the capillaries are disposed in the temperature adjusted gas so as to adjust the temperature of the capillaries; and a liquid temperature adjustment method in which temperature adjusted liquid such as water is circulated in a vessel provided in the electrophoresis apparatus and the capillaries are disposed in the temperature adjusted liquid so as to adjust the temperature of the capillaries.
The contact temperature adjustment method in which the capillaries are directly contacted to the temperature control plate provided with a heating and cooling device such as Peltier elements shows an advantage that Joule's heat generated at the capillaries during electrophoresis is effectively removed from the capillaries. However, since a fine temperature variation of the temperature control plate is directly transmitted to the capillaries, it is necessary to control the temperature of the temperature control plate strictly at a predetermined temperature. However, a temperature variation could not be avoided, because a power source is frequently turned on and off for the temperature control.
The liquid temperature adjustment method shows an advantage that the Joule's heat generated at the capillaries is effectively removed from the capillaries. However, since the liquid has to be circulated in the apparatus which complexes the apparatus and increases the cost thereof.
The gas circulation method, for example, the air conditioning method and the air circulation method shows advantages that the structure of the electrophoresis is simple and further because of existence of air between the capillaries and a heater portion in the thermostatic oven an influence of heater temperature fluctuation affected on the capillaries is relaxed. However, since the heat conduction from the capillaries to air is small, the heat dissipation of the Joule's heat generated from the capillaries is insufficient. The insufficient heat dissipation from the capillaries will affect the electrophoresis speed and causes an adverse effect to the analysis result.